fix --backfill-oldest-slot flag handling (#14584)

* fix --backfill-oldest-slot flag handling

* changelog

---------

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>

CHANGELOG.md

@@ -49,6 +49,7 @@ The format is based on Keep a Changelog, and this project adheres to Semantic Ve
 - Certain deb files were returning a 404 which made building new docker images without an existing
   cache impossible. This has been fixed with updates to rules_oci and bazel-lib.
 - Fixed an issue where the length check between block body KZG commitments and the existing cache from the database was incompatible.
+- Fix `--backfill-oldest-slot` handling - this flag was totally broken, the code would always backfill to the default slot [pr](https://github.com/prysmaticlabs/prysm/pull/14584)
 
 ### Security
 

cmd/beacon-chain/sync/backfill/options.go

@@ -19,7 +19,7 @@ func BeaconNodeOptions(c *cli.Context) ([]node.Option, error) {
 		}
 		// The zero value of this uint flag would be genesis, so we use IsSet to differentiate nil from zero case.
 		if c.IsSet(flags.BackfillOldestSlot.Name) {
-			uv := c.Uint64(flags.BackfillBatchSize.Name)
+			uv := c.Uint64(flags.BackfillOldestSlot.Name)
 			bno = append(bno, backfill.WithMinimumSlot(primitives.Slot(uv)))
 		}
 		node.BackfillOpts = bno